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Branching Ratios and Angular Distribution of B  D*  Decays

Branching Ratios and Angular Distribution of B  D*  Decays. Istv á n Dank ó Rensselaer Polytechnic Institute (CLEO Collaboration) July 17, 2003 EPS Int. Europhysics Conference on HEP Aachen, Germany. CESR. CLEO. Outline. Motivation CLEO detector and data Event Selection

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Branching Ratios and Angular Distribution of B  D*  Decays

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  1. Branching Ratios and Angular Distribution of B  D* Decays István Dankó Rensselaer Polytechnic Institute (CLEO Collaboration) July 17, 2003 EPS Int. Europhysics Conference on HEP Aachen, Germany CESR CLEO

  2. Outline • Motivation • CLEO detector and data • Event Selection • Maximum Likelihood Fit • Results: • Branching Fractions • Helicity Amplitudes • Conclusion EPS Abstract: 119 CLEO Collaboration, S. E. Csorna et al., Phys. Rev. D. 67, 112002 (2003)

  3. Hadronic decays are complicated by final-state interactions. Factorization hypothesis (FH): the products of two-body B meson decays hadronize independently. The validity of the FH has to be tested experimentally. If FH is valid then certain 2-body hadronic decays are analogous to similar semileptonic decays: Experimental tests: Comparing decay rates, Comparing the polarization of the B0D*+ decay to that of the B0D*+l decay at the same momentum transfer (q2=M2=Ml2 ). J. Körner and G. Goldstein, Phys. Lett 89B, 105 (1979) l u  W W  d b b c c D*+ D*+ d d d d Motivation

  4. B  D* Decay • Color-enhanced diagram (a1) • Color-suppressed diagram (a2) Color-allowed Color-suppressed • Color-enhanced diagram (a1) Relative effective coupling strength in BSW model: Color-allowed M. Bauer, B. Stech, and M. Wirbel, Z. Phys. C 34, 103 (1987)

  5. B  D* : Angular Distribution • Three possible helicity final states (P  VV decay): • Angular distribution is described by the coherent sum of the three helicity states: H0, H+, H- : complex helicity amplitudes (H=|H|ei) • Previous CLEO measurements: • Phys. Rev. D 50, 43 (1994): 0.89 fb-1 data, (cosD*,cos) • CLEO CONF 98: 3.1 fb-1 data, (cosD*,cos, )

  6. 9.1 fb-1 (9.7 million BB pairs) 4.6 fb-1 to study background CLEO detector and data sample • The data were collected by the CLEO II/II.V detector at the Cornell Electron Storage Ring (CESR). • CLEO II: • Tracking Chambers (1.5T B, 95% 4), • TOF, • CsI EM Calorimeter (98% 4), • Muon detectors (85% 4) • CLEO II.V: • Si Vertex Detector, • He-Propane DR gas. BB threshold On-res. Off-res.

  7. Charge track selection: If p > 250 MeV: Originate from interaction point and well measured dE/dx consistent with K or  hypothesis within 2.5 No lepton If p < 250 MeV (from D* and D0) Only loose requirement of consistency with originating from interaction point 0 selection: Photon pair in barrel calorimeter E > 30-65 MeV (mode dependent) | M - M0 | < 2.5 D0 selection: | MK(n) – MD0 | < 2.5 D0K+0 : densely populated region of the Dalitz plot D*0 and D*+ selection: | M  MPDG | < 2.5 (M = MD*  MD0) - selection: | M  M | < 150 MeV/c2 B selection: Background suppression: Fox-Wolfram moment R2 < 0.5 | cos S | < 0.7-0.9 | cos B | < 0.95 Event reconstruction and selection criteria

  8. Maximum Likelihood Fit • Unbinned maximum likelihood fit: • j = njS + njB number of signal and background events in the jth D0 decay mode, • Probability density function (pdf): Signal pdf: MB: Gaussian distribution for M: Breit-Wigner with Blatt-Weiskopf form-factor A: angular distribution corrected by detector acceptance Background pdf: MB: ARGUS-type function M: flat distribution A : 2nd order polynomials in cosD* and cos,1st order polynomial of cos(+0)) • Two-step fit: • For signal and background and mass distribution parameters (no angular part); • For helicity amplitudes (signal, background and mass parameters are fixed).

  9. 1st Syst. Error 2nd Syst. Error Branching Ratio • To extract number of signal and background events: maximum likelihood fit to all events with 5.2 < MB < 5.3 GeV/c2 (angular distribution ignored) • NBB 2% • background shape  3% • efficiency  10  18% • D* and D0 • Br ratio error

  10. Branching Ratio • Comparison with previous results: • BSW effective couplings: 3rd syst. error is from f+-/f00=1.0720.0450.0270.024 (PDG 02)

  11. Helicity Amplitudes • Maximum likelihood fit including events with 5.27 < M < 5.30 GeV/c2 only: • njS , njB (scaled) and mass distribution parameters are fixed, • helicity parameters (|H+|, |H|, +-0, -0) are allowed to float in the fit (|H0|2+|H+|2+|H|2=1, and 0=0), • Detector acceptance depends on the polarization (angular distribution) due to detector smearing  needs iteration until helicity amplitudes converge.

  12. Helicity Amplitudes • Helicity amplitudes (H=|H|ei) |H0|2+|H+|2+|H|2=1 • Systematic uncertainties: • Acceptance parametrization • Detector smearing • Background level/shape (dominant) • Non-resonant 0 contribution • Polarization dependence on m • Non-trivial helicity amplitude phases (+ , ) Significance: • Indication of FSI • Important for direct CPV in B decay

  13. Longitudinal Polarization • Longitudinal polarization: • Previous CLEO measurements of long. polarization in B0D*+: (1994) (1998) • HQET with factorization: Consistent with measurement! B0D*+’: CLEO Coll., PRD 64, 092001 (2001); B0 D*+DS*: CLEO Coll., PRD 62, 112003 (2000)

  14. Conclusion • CLEO has measured the branching ratio and helicity amplitudes of the decays BD*0 and B0D*+. • Calculated the the ratio of effective coupling constants a2/a1 and the degree of longitudinal polarization. • The fraction of longitudinal polarization for B0D*+ decay confirms the validity of the factorization hypothesis at relatively low q2: • Measurement of the helicity amplitudes indicates a strong possibility of non-trivial helicity amplitude phases which would arise from final-state interactions (indication of FSI has been reported in BJ/K* by CDF (PRL 85, 4668 (2000) and BD by CLEO (PRL 88, 062001 (2002) ) • CLEO Collaboration, Phys. Rev. D 67, 112002 (2003)

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